Effect of Habitual Diet on Fuel Utilisation During Exercise

Abstract

The aim of the work presented in this thesis was to determine the effect of varying dietary macronutrient contributions, specifically carbohydrate and fat, on fuel utilisation during exercise. This was first investigated through a systematic review of the literature addressing how habitual diets (>4 weeks) with differing fat contributions affect fuel utilisation (fat oxidation, carbohydrate oxidation and RER) during aerobic exercise and whether it also affects aerobic capacity and endurance performance. Secondly, a cross-sectional study was conducted to determine the effects of carbohydrate on the maximal amount of fat able to be oxidised during exercise in a general population, as well as various health measures of participants with carbohydrate restriction below recommended dietary guidelines. The systematic review demonstrated increased fat oxidation during exercise when consuming a high fat diet. There was no improved aerobic capacity or endurance performance due to increased dietary fat, and occasionally resulted in decreased performance. The longer the dietary intervention, and the larger the increase in dietary fat as well as decrease in dietary carbohydrate resulted in greater increases in fat oxidation, larger reductions in RER and was less likely to negatively impact performance. The cross-sectional study showed a negative correlation between dietary carbohydrate and maximal fat oxidation. This relationship was stronger when comparing extreme carbohydrate restriction to carbohydrate consumption within normal dietary guidelines. Health outcomes were very similar between the two dietary groups.